This invention relates to an improvement in the separability, in sequence, of individual top charts from a stacked array of such charts mounted on a chart-driving and changing mechanism. Such chart-driving and changing mechanisms are well known in the prior art. A motor is used to rotate the chart-carrying apparatus, and a complete rotation of the chart occurs over a predetermined cyclical time period. Typically, the cyclical period is one, twenty-four (24) hour day. Several charts are carried on a support shaft of the chart drive mechanism as a stacked array so that successive charts can be sequentially rotated through the predetermined time period for the recordation of time-correlated data thereon. In each time period, data are recorded on the face of the top chart. At the end of each time cycle, the chart drive mechanism should automatically eject the completed chart into a storage hopper. Data will then be recorded on the next chart of the array.
A crucial functional element of the mechanism in the separation of the top chart from the stacked array of charts is a rotatably shiftable hub or release button having a blade-like edge or terminus which rotates periodically, in a plane generally paralleling a plane of the top chart. At the end of the predetermined recording period, a tensioned spring of the mechanism releases the release button to execute a rotational shift. A lip of the blade-like terminus of the release-button is received beneath the top chart. The rotating release button thus displaces or lifts the top chart from the stacked array, and the top chart is demounted from the support shaft and falls into a storage receptacle.
Ordinary chart paper of the type used in connection with chart changing mechanisms as described are subject to several difficulties. Occasionally, the lip of the blade-like terminus of the rotating hub or release button will encounter the lateral edge of the paper rather than being received beneath the top chart. The blade-like terminus will then cut into the chart and the chart will not be separated from the stacked array of charts therebeneath. As a result, the next period's data will be imprinted or scribed on the same chart as were the previous time period's data. Several change periods may go by before the problem is noted and valuable data could be irretrievably lost. A proposal for reducing the likelihood of chart changing failure is described in U.S. Pat. No. 4,224,629 which discloses a chart recording paper to which a piece of plastic reinforcement has been fitted at a button-presented chart edge. However, this structural chart modification requires a second separate step of placing the reinforcement to envelop the chart edge. The patentee describes no economical way of making the suggested chart modification.